1. Field
One or more embodiments relate to a quantum dot light emitting device, and more particularly, to a quantum dot light emitting device having a quantum dot multilayer including quantum dots.
2. Description of the Related Art
Organic light emitting devices (“OLEDs”) typically have a multilayered thin film structure mainly formed of a low molecular weight organic material. A display device using such an OLED has certain advantages such as a variety of materials may be selected for forming an internal thin film, a high purity thin film may be formed and a high light emitting performance may be obtained therefrom. In contrast, there are problems and disadvantages associated with the use of an OLED such as oxidation or crystallization of the OLED through reaction with an external toxic material and the manufacturing of an OLED includes a complicated and expensive film formation process because the OLED is typically formed at a predetermined position using vacuum deposition.
Recently, research focus on a light emitting device using the light emitting characteristic of a quantum dot (“QD”) has increased. A QD is a particle formed of a semiconductor material having a crystal structure of a size smaller than the radius of a Bohr exciton, that is, the typical QD is only several nanometers in size. Although numerous electrons exist in the QD, the number of free electrons is limited to about 1-100. In this case, the energy levels of electrons are discontinuously limited so that electric and optical characteristics of the QD may be different from those of a semiconductor in a bulk state forming a continuous band. Since the energy level of the QD varies according to the size thereof, a band gap, and therefore an energy of a photon resulting from the band gap, may be controlled by simply changing the size of the QD. That is, the light emitting wavelength of the QD may be adjusted by simply adjusting the size thereof.
A typical quantum dot light emitting device (“QD-LED”), in which the QD is used for forming a light emitting layer, has a basic structure of three layers, that is: a QD light emitting layer, and a hole transport layer (“HTL”) and an electron transport layer (“ETL”) which are respectively located at either end of the QD light emitting layer.